1. Field of the Invention
This invention relates generally to internally threaded members such as threaded buttress collars and more particularly, to a method for removing feather edge threads from internally threaded and grooved members.
2. Brief Description of the Prior Art
There is in the prior that which is typically referred to as the API buttress collar. API buttress collars are often modified such that spaced from each face of the collar, there is machined or cut within the buttress collar an annular groove which provides residence for a seal ring. When such seal ring grooves are cut into a threaded collar, there are created feather edge threads immediately adjacent the seal ring groove. These feather edge threads at their beginning points are literally thinner than ordinary paper and are therefore easily deformable. The feather edge threads may be deflected by the jarring contact between the threads of the male and female members when they are being screwed together, or they may be deflected merely by the manual insertion of the seal rings within the grooves. The feather edge threads may also be be deflected by the pressure of the seal ring when the male member is screwed into the coupling. As the seal ring is engaged by the threads of the male member it is caused to flow about the threads of the male member. Assuming proper selection of seal ring design, the volume of the seal ring is greater than the volume of the groove minus the volume of the threads of the male member residing in the seal ring groove. In other words, proper selection of seal ring design will create a slight overfill condition. The net result is that the seal ring flows against and places pressure upon the feather edge thread adjacent the seal ring groove. This pressure is significant and easily deflects the feather edge thread into the path of the threads of the male member. The resulting collision between the feather edge thread and the threads of the male member creates a galling problem from that point on within the coupling. This galling problem can cause two distinct effects. Galling can decrease the leak resistance of the connection between the male and female members. Galling can also decrease the tensional loading capacity of the connection.
There is in the prior art a variety of improved coupling and threaded pipe joint connections having groove and seal rings therein. However, none of these prior art teachings deal with the problem created by the feather edge thread nor do they teach any method for removing the feather edge thread to alleviate the problem.
For example, U.S. Pat. No. 2,150,221 to Hinderliter teaches a rotary tool joint having dual seal retaining grooves. Such grooves are machined into the coupling at substantially the starting and ending points of the threads. However, Hinderliter does not recognize the problem created by machining a groove in an internally threaded member thereby creating a feather edge thread and therefore offers no solution to such problem.
Similarly, U.S. Pat. No. 2,980,451 to Taylor et al teaches a threaded pipe joint having an extrudable sealing means residing within a seal ring groove. As such, Taylor et al teaches nothing more then what can be seen from the typical modified API threaded buttress collar previously mentioned. It is not directed to the problem created by placing a seal ring groove within an internally threaded member and teaches nothing with regard to the solution of such problem.
U.S. Pat. No. 4,431,219 to Brewer et al teaches a replaceable tubular connector. Such replaceable tubular connector has machined therein what is referred to as an annular groove in which mounts a deformable seal ring. Brewer et al does not address the problem created by machining an annular groove within an internally threaded member to create an easily deformable feather edge thread and therefore, offers no solution to such problem.
While there is a feather edge thread on each side of each seal ring groove, it is that feather edge thread furthest from the face of the collar which is the source of the galling problem. Methods and operations to remove the deflectable portion of such feather edge threads are heretofore unknown.